1. Field of the Invention
This invention relates to signal processing. Specifically, the present invention relates to digital signal processing.
2. Description of the Related Art
Signal processing involves the manipulation or processing of signals. Signal processing research and technology were initially directed at analog signals. However, as technology improved, digital technology was implemented and digital signal processing emerged as a technology field. In digital signal processing, digital samples are manipulated or processed.
One area of signal processing focuses on the filtering or removal of noise from a signal. An analog signal is graphically represented as a continuous wave. Analog signal noise is typically represented as a positive or negative spike in a continuous wave. A large variety of signal processing techniques have been developed to remove spikes (i.e., noise) from a continuous wave.
A similar type of processing occurs with digital signals. Digital signals are often represented as a logical 0 or a logical 1. A digital signal is typically a discrete sampling of an analog signal. Noise may change a logical 0 to a logical 1 or a logical 1 to a logical 0. As a result, techniques have developed to remove noise from digital signals.
One technique for removing noise from both analog and digital signals uses a filter. The filter is considered a high pass filter when the filter removes low frequency noise and the filter is considered a low pass filter when the filter removes high frequency noise spikes. However, these filters are often implemented with complex circuitry.
Implementing complex circuits into silicon or some other type of semiconductor material is costly. In addition, since space is at a premium in most semiconductor devices, the more logic gates required to implement a device (i.e., digital filter), the more costly the device will be.
In addition, many digital filters are designed to process a signal that rises/falls uniformly. However, many real world signals do not rise and fall uniformly. Further, when noise affects a signal, it may not affect the signal in the same way on the rising edge of the signal as on the falling edge of the signal. Consequently, many signal processing designs are implemented with combination filters that perform a combination of high pass and low pass functions. As mentioned previously, these filters are implemented with complex digital logic and require a substantial amount of space on a semiconductor device, and as a result, they are costly to implement.
Thus, there is a need for a method and apparatus for performing digital signal processing. There is a need for a method and apparatus for filtering signals, which can be implemented with a simple digital logic design. Lastly, there is a need for a method and apparatus that will filter both a rising and falling signal.